OH!!!!!! FINALLY I MANAGE TO MAKE IT WORKING!!!!!
The problem is with the modded version of SETUPDS.EXE. I thought I have to use the ICH2 version, since I use the CUSL2-C mobo. The standard SETUPDS has all the settings related to SB greyed out. So I thought it wouldn't work. The turning point is when I saw there is a file called "dsxgdos_ms-dos__restart_in_ms-dos_mode_in_win_95_98__v._3.16.exe" in Philscomputerlab's site. I downloaded it, installed it and tried it with Windows 98 DOS Mode and it worked! The installation included the standard SETUPDS.EXE. I got it working just by launching the Loadtsr.bat. Actually after the SB emulation worked, I run the SETUPDS itself again and the error "CODEC might not be connected" is still there with my newly bought Genius Soundmaker 128XG (ymf724). This made thinking the error message is not a problem at all. So I restart the PC to the pure DOS, which is isolated from Windows, run the Loadtsr.bat, then fire up DOOM, I then heared the digital sound! What a stubborn card!
Thank you all and thank you @wbahnassi! It's really a tricky one to deal with.
I want to tell all the people who loves ymf7x4 cards and have the CUSL2-C mobo. It is compatible with the card by using DSDMA!
BUT DON'T USE THE ICH2 MODDED SETUPDS.EXE!!!!!
It seems promising(SB related options are white), but it will NEVER work!